Marble Hornets was a popular YouTube horror webseries that went from June 20, 2009 to June 20, 2014, created by Troy Wagner, Joseph DeLage, and Tim Sutton. It was the first series to show the popular Internet character Slender Man (created by Eric Knudsen) in video format. Slender Man (Known as just "The Operator" in Marble Hornets) first became popular with this series, and many of the traits that would be associated with him (Like visual distortion) would come from this series.
Marble Hornets was very influential on amateur horror YouTube content, including other Slender Man YouTube series like EverymanHYBRID, TribeTwelve, DarkHarvest00, and MLAndersen0. After the series ended, there was a film made, Always Watching: A Marble Hornets Story (2015) that was not well-received by fans and critics. There was also a comic series written by creator Troy Wagner that continues the series.
Marble Hornets follows Jay (Troy Wagner), a former film student who decides to go through and upload tapes from a student film he helped worked on 3 years ago. The film was called Marble Hornets, and it was directed by Jay's friend Alex Kralie (Joseph DeLage).
The film was never completed due to Alex's erratic behavior during shooting, and Alex gives the tapes to Jay. As Jay goes through the tapes, he notices something stalking Alex...